function [b,a]=ellipfilter(freq)

center = freq/4000;
Wp = [center-0.001 center+0.001]; Ws = [center-73/4000 center+73/4000];
Rp = 0.2; Rs = 1;
% Cauer (elliptic) filter
[n,Wn] = ellipord(Wp,Ws,Rp,Rs);
[b,a] = ellip(n,Rp,Rs,Wn); % transfer function sum(b(i)/1+a(i))
